• Title, Summary, Keyword: Organic light-emitting diodes

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Efficient Deep-Blue Organic Light-emitting Diodes with Double-Emission Layers

  • Seo, Ji-Hoon;Park, Jung-Sun;Seo, Bo-Min;Lee, Kum-Hee;Park, Jung-Keun;Yoon, Seung-Soo;Kim, Young-Kwan
    • Journal of Information Display
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    • v.10 no.3
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    • pp.107-110
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    • 2009
  • Efficient deep-blue organic light-emitting diodes were demonstrated using 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl doped in double-emission layers (D-EMLs). The D-EML system, which consists of 2-methyl-9,10-di(2-naphthyl)anthracene and 1,4-(dinaphthalen-2-yl)-naphthalene as blue hosts, was employed to broaden the recombination zone and to ensure the good confinement of the holes and electrons. The optimized device showed a peak current efficiency of 4.47 cd/A, a peak external quantum efficiency of 4.09%, and Commission Internationale de L'Eclairage coordinates of (0.16, 0.10).

Performance Enhancement of Organic Light-emitting Diodes with an Electron-transport Layer of Bathocuproine

  • Honga, Jin-Woong;Guo, Yi-Wei;Shin, Jong-Yeol;Kim, Tae Wan
    • Transactions on Electrical and Electronic Materials
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    • v.17 no.1
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    • pp.37-40
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    • 2016
  • Performance enhancement of organic light-emitting diodes (OLEDs) is investigated in a device structure of ITO/TPD/Alq3/LiF/Al and ITO/TPD/Alq3/BCP/LiF/Al. Here, bathocuproine (BCP) is used as an electron-transport layer. Current density-voltage-luminance characteristics of the OLEDs show that the performance of the device is better with BCP layer than without BCP layer. The current density, luminance, luminous efficiency, and external-quantum efficiency are improved by approximately 22%, 50%, 2%, and 18%, respectively. Since the BCP layer lowers the electron energy barrier, electron transport is facilitated and the movement of hole is blocked as the applied voltage increases. This results in an increased recombination rate of holes and electrons.

Effects of PEDOT:PSS Buffer Layer in a Device Structure of ITO/PEDOT:PSS/TPD/Alq3/Cathode

  • Ahn, Joon-Ho;Lee, Joon-Ung
    • Transactions on Electrical and Electronic Materials
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    • v.6 no.1
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    • pp.25-28
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    • 2005
  • We have investigated the effects of hole-injection buffer layer in organic light-emitting diodes using poly(3,4-ethylenedioxythiophene):poly(stylenesulfonate)(PEDOT:PSS) in a device structure of $ITO/PEDOT:PSS/TPD/Alq_{3}/cathode$. Polymer PEDOT:PSS buffer layer was made by spin casting method. Current-voltage, luminance-voltage characteristics and efficiency of device were measured at room temperature with a variation of cathode materials; Al, LiF/Al, LiAl, and Ca/Al. The device with LiF/Al cathode shows an improvement of external quantum efficiency approximately by a factor of ten compared to that of Al cathode only device. Our observation shows that cathode is important in improving the efficiency of the organic light-emitting diodes.

Electrical Conduction Mechanism in ITO/Alq3/Al Organic Light-emitting Diodes

  • Chung, Dong-Hoe;Lee, Joon-Ung
    • Transactions on Electrical and Electronic Materials
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    • v.5 no.1
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    • pp.24-28
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    • 2004
  • We have used ITO/Alq$_3$/Al structure to study electrical conduction mechanism in organic light-emitting diodes. Current-voltage-luminance characteristics were measured at room temperature by varying the thickness of Alq$_3$ layer from 60 to 400mm. We were able to confirm that there are three different mechanisms depending on the applied voltage region; ohmic, space-charge-limited current, and trap-charge-limit-current mechanism. And the maximum luminous efficiency was obtained when the thickness of Alq$_3$ layer is 200nm.

Current-Voltage Characteristics of Organic Light-Emitting Diodes with a Variation of Temperature (온도 변화에 따른 유기 전기 발광 소자의 전압-전류 특성)

  • Kim, Sang-Geol;Hong, Jin-Ung;Kim, Tae-Wan
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.51 no.7
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    • pp.322-327
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    • 2002
  • Temperature-dependent current-voltage characteristics of organic light-emitting diodes(OLEDs) were studied in a device structure of ITO/TPD/Alq$_3$/Al to understand conduction mechanism. The current-voltage characteristics were measured in the temperature range of 8K ~ 300K. We analyzed an electrical conduction mechanism of the OLEDS using space-charge-limited current(SCLC) and Fowler-Nordheim tunneling. In the temperature range above 150k, the conduction mechanism could be explained by space charge limited current from the inversely proportional temperature dependence of exponent m. The characteristic trap energy is found to be about 0.15ev. At low temperatures below 150k, the Fowler-Nordheim tunneling conduction mechanism is dominant. We have obtained a zero field barrier height to be about 0.6~0.8eV.

A Study on the Dielectric Polarization of $ITO/Alq_3/Al$ Structure Organic Light-emitting Diodes ($ITO/Alq_3/Al$ 구조 유기 발광 소자의 유전분극 현상의 연구)

  • Oh, Yong-Cheul;Shin, Cheol-Gi;Kim, Chung-Hyeak
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.57 no.1
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    • pp.73-77
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    • 2008
  • We have investigated dielectric polarization in organic light-emitting diodes using 8-hydroxyquinoline aluminum($Alq_3$) as an electron transport and emissive material. We analyzed the dielectric polarization of organic light-emitting diodes using characteristics of impedance and equivalent circuit of $ITO/Alq_3/Al$. Impedance characteristics was measured complex impedance Z and phase ${\theta}$ in the frequency range of $1{\times}40Hz\;to\;1{\times}10^8Hz$. We obtained complex electrical conductivity, dielectric constant, and loss tangent(tan${\delta}$) of the device at room temperature. And, we obtained the equivalent circuit of $ITO/Alq_3/Al$ through analyzing dielectric constant and dielectric loss tangent. From these analyses, we could interpret a conduction mechanism and dielectric polarization.

Indium Tin Oxide Thin Films Grown on Polyethersulphone (PES) Substrates by Pulsed-Laser Deposition for Use in Organic Light-Emitting Diodes

  • Kim, Kyung-Hyun;Park, Nae-Man;Kim, Tae-Youb;Cho, Kwan-Sik;Sung, Gun-Yong;Lee, Jeong-Ik;Chu, Hye-Yong
    • ETRI Journal
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    • v.27 no.4
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    • pp.405-410
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    • 2005
  • High quality indium tin oxide (ITO) thin films were grown by pulse laser deposition (PLD) on flexible polyethersulphone (PES) substrates. The electrical, optical, and surface morphological properties of these films were examined as a function of substrate temperature and oxygen pressure. ITO thin films, deposited by PLD on a PES substrate at room temperature and an oxygen pressure of 15 mTorr, have a low electrical resistivity of $2.9{\times}10^{-4}{\Omega}cm$ and a high optical transmittance of 84 % in the visible range. They were used as the anode in organic light-emitting diodes (OLEDs). The maximum electro luminescence (EL) and current density at 100 $cd/m^2$ were 2500 $cd/m^{2}$ and 2 $mA/m^{2}$, respectively, and the external quantum efficiency of the OLEDs was found to be 2.0 %.

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Improved Performance of White Phosphorescent Organic Light-Emitting Diodes through a Mixed-Host Structure

  • Lee, Jong-Hee;Lee, Jeong-Ik;Chu, Hye-Yong
    • ETRI Journal
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    • v.31 no.6
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    • pp.642-646
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    • 2009
  • Highly efficient white phosphorescent organic light-emitting diodes with a mixed-host structure are developed and the device characteristics are studied. The introduction of a hole-transport-type host (N, N'-dicarbazolyl-3-3-benzen (mCP)) into an electron-transport-type host (m-bis-(triphenylsilyl)benzene (UGH3)) as a mixed-host emissive layer effectively achieves higher current density and lower driving voltage. The peak external quantum and power efficiency with the mixed-host structure improve up to 18.9% and 40.9 lm/W, respectively. Moreover, this mixed-host structure device shows over 30% enhanced performance compared with a single-host structure device at a luminance of 10,000 $cd/m^2$ without any change in the electroluminescence spectra.

Current-Voltage-Luminance Characteristics Depending on a Direction of Applied Voltage in Organic Light-Emitting Diodes

  • Kim, Sang-Keol;Hong, Jin-Woong;Kim, Tae-Wan
    • Transactions on Electrical and Electronic Materials
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    • v.3 no.1
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    • pp.38-41
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    • 2002
  • We have investigated current-voltage-luminance characteristics of organic light-emitting diodes based on TPD/Alq$_3$organics depending on the application of forward-backward bias voltage. Luminance-voltage characteristics and luminous efficiency were measured at the same time when the current-voltage characteristics were measured. We have observed that the current-voltage characteristics shows a reversible current maxima at low voltage, which is possibly not related to the emission from Alq$_3$. Current-voltage-luminance characteristics imply that the conduction luminance mechanism at low voltage is different from that of high voltage one.

Fully Solution-Processed Green Organic Light-Emitting Diodes Using the Optimized Electron Transport Layers (최적화된 전자 수송층을 활용한 완전한 용액공정 기반 녹색 유기발광다이오드)

  • Han, Joo Won;Kim, Yong Hyun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.31 no.7
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    • pp.486-489
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    • 2018
  • Solution-processed organic light-emitting diodes (OLEDs) have the advantages of low cost, fast fabrication, and large-area devices. However, most studies on solution-processed OLEDs have mainly focused on solution-processable hole transporting materials or emissive materials. Here, we report fully solution-processed green OLEDs including hole/electron transport layers and emissive layers. The electrical and optical properties of OLEDs based on solution-processed TPBi (2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) as the electron transport layer were investigated with respect to the spin speed and the number of layers. The performance of OLEDs with solution-processed TPBi exhibits a power efficiency of 9.4 lm/W. We believe that the solution-processed electron transport layers can contribute to the development of efficient fully solution-processed multilayered OLEDs.